This application is based on Japanese Patent Application No. 2001-205261 filed on Jul. 5, 2001, the disclosure of which is incorporated herein by reference.
The present invention relates to a method for manufacturing a heat exchanger having different heat capacity in partial. The heat exchanger includes a core portion having plural tubes through which a thermal medium flows and plural radiation fins connected to surfaces of the tubes, and a tank portion communicating with the tubes.
In a manufacturing method for manufacturing a heat exchanger composed of a core portion and a tank portion communicating with tubes of the core portion, the tank portion and the tubes are bonded by brazing, and radiation fins are bonded onto the tubes between adjacent tubes by the brazing. Therefore, a brazing filler-metal material having a flux thereon is disposed at bonding parts of the members such as the tubes, the radiation fins and the tank portion to assemble the members. Specifically, a preheating step, a brazing step, a gradual cooling step and a cooling step are performed in this order. An assembly of the members are heated until the flux is melted in the preheating step, and are heated until the brazing filler-metal material is melted in the brazing step. Then, the gradual cooling step is performed until the brazing filler-metal material is solidified. Next, the cooling step is performed until the temperature of the heat exchanger becomes room temperature.
The heat exchanger includes a thinner part such as a core portion having a small heat capacity, and a thicker part such as the tank portion having a large heat capacity. Therefore, it is difficult to uniformly increase the temperature of the entire assembly when the assembly is heated in the preheating step. Further, in the preheating step, it is necessary to continuously heat the assembly until the temperature of the thicker part having the large heat capacity is increased to a brazing temperature after the thinner part having the small heat capacity reaches the brazing temperature. Accordingly, heating time in the preheating step becomes longer, and production efficiency is deteriorated. Further, since the brazing filler-metal material (especially, Si in the brazing material) is moved in a plate thickness direction or is moved to the thin part such as the radiation fins, erosion may be caused. Therefore, the radiation fins may be melted, and durability of the heat exchanger may be deteriorated.
In view of the foregoing problems, it is an object of the present invention to provide a manufacturing method for manufacturing a heat exchanger, which improves durability of the heat exchanger while improving product efficiency thereof.
A manufacturing method according to the present invention is suitably used for a heat exchanger including a core portion having a plurality of tubes and a plurality of radiation fins connected to surfaces of the tubes, and a tank portion communicating with the tubes. The manufacturing method includes: preheating the heat exchanger until a temperature where a flux in the heat exchanger is melted, heating the heat exchanger after the preheating until a temperature where a brazing filler-metal material (brazing material) in the heat exchanger is melted, and cooling the heat exchanger after the heating. The cooling can include a first cooling step for gradually cooling the beat exchanger after the heating to a temperature where the brazing filler-metal material is solidified, and a second cooling step for further cooling the heat exchanger to a room temperature after the first cooling step. In addition, in the preheating, a temperature of a first part of the heat exchanger, having a heat capacity larger than a predetermined capacity, is increased earlier than a temperature of a second part of the heat exchanger, having a heat capacity smaller than the predetermined capacity. Accordingly, in the preheating, the temperature of the tank portion is increased to be equal to or higher than that of the core portion, and the temperature of the core portion is obediently increased in accordance with the temperature increase of the tank portion. Thus, it can prevent an erosion from being caused in the heat exchanger.
When the first part is the tank portion, and the second part is the core portion, the manufacturing method improves durability of the core portion of the heat exchanger and improves production efficiency thereof.
Preferably, in the preheating, a high-temperature gas is blown toward the first part to increase the temperature of the first part earlier than that of the second part. Therefore, the temperature of the first part having the large heat capacity can be readily increased earlier than the temperature of the second part.
Preferably, in the preheating, the high-temperature gas has a temperature equal to higher than 450xc2x0 C., or/and the high-temperature gas is blown toward the first part by a flow speed equal to or larger than 5 m/second. Therefore, a thermal increase time of the first part having the large heat capacity can be shortened without reducing the durability of the heat exchanger.